Ellicottville Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ellicottville Observatory clear sky chart from 2005-11-06 to 2024-08-30.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	16% 14% 5% 10% 5% 4 4 4 5% 6% 27%	95746
	Night	16% 16% 6% 11% 6% 4 4 3 4 5% 26%	93290
Transparency	Day	56% 6% 11% 18% 9% 1	95475
	Night	59% 5% 10% 16% 8% 1	93115
Seeing	Day	26% 18% 28% 17% 9% 3	14337
	Night	25% 17% 26% 22% 9% 1	23742

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	13% 25% 14% 16% 7% 3 3 2 2 4 11%	2517
	11th to 20th	Day	11% 23% 10% 22% 7% 3 2 2 2 3 14%	2790
	21st to end	Day	21% 19% 9% 19% 8% 5% 3 3 3 3 7%	3124
February	1st to 10th	Day	15% 22% 7% 17% 9% 5% 4 2 3 3 14%	1710
	11th to 20th	Day	13% 17% 8% 19% 8% 4 4 3 4 3 15%	1663
	21st to end	Day	18% 17% 6% 13% 7% 4 3 3 4 5% 19%	1500
March	1st to 10th	Day	18% 15% 8% 10% 4 3 3 3 4 5% 27%	3432
	11th to 20th	Day	10% 23% 8% 10% 4 3 4 3 4 6% 26%	3480
	21st to end	Day	18% 14% 6% 13% 5% 4 4 3 4 5% 25%	3815
April	1st to 10th	Day	16% 18% 5% 8% 5% 4 4 3 4 6% 27%	2267
	11th to 20th	Day	19% 15% 3 6% 3 3 4 4 5% 6% 32%	2254
	21st to end	Day	21% 13% 3 8% 5% 3 4 3 4 5% 31%	2454
May	1st to 10th	Day	23% 11% 3 7% 4 4 4 3 5% 6% 30%	4108
	11th to 20th	Day	18% 11% 3 9% 5% 5% 6% 4 6% 7% 26%	4356
	21st to end	Day	13% 7% 2 6% 5% 5% 5% 4 6% 8% 40%	4837
June	1st to 10th	Day	18% 9% 2 7% 5% 4 4 4 6% 8% 34%	2660
	11th to 20th	Day	16% 8% 2 7% 5% 4 5% 5% 6% 8% 33%	2660
	21st to end	Day	17% 6% 2 6% 4 5% 6% 4 6% 8% 35%	2660
July	1st to 10th	Day	11% 6% 2 7% 5% 5% 6% 5% 8% 9% 35%	4440
	11th to 20th	Day	13% 7% 2 6% 5% 5% 5% 5% 8% 10% 35%	4440
	21st to end	Day	9% 7% 3 8% 6% 5% 6% 5% 7% 8% 36%	4466
August	1st to 10th	Day	13% 6% 3 7% 5% 5% 5% 5% 8% 9% 35%	2457
	11th to 20th	Day	13% 8% 3 8% 6% 6% 6% 5% 7% 9% 28%	2433
	21st to end	Day	15% 7% 2 7% 4 5% 6% 4 6% 9% 34%	2533
September	1st to 10th	Day	18% 8% 3 7% 4 3 5% 4 6% 8% 34%	2160
	11th to 20th	Day	16% 7% 3 5% 5% 4 5% 4 6% 8% 38%	2098
	21st to end	Day	18% 9% 4 8% 5% 4 5% 4 5% 7% 30%	1916
October	1st to 10th	Day	23% 9% 3 8% 5% 4 4 3 5% 6% 31%	1800
	11th to 20th	Day	23% 15% 4 8% 5% 4 4 3 3 5% 27%	1800
	21st to end	Day	26% 19% 4 8% 3 4 4 3 4 4 21%	1980
November	1st to 10th	Day	14% 20% 4 7% 5% 5% 3 3 5% 6% 28%	1698
	11th to 20th	Day	15% 25% 6% 9% 4 3 3 4 4 6% 20%	1520
	21st to end	Day	18% 26% 7% 11% 4 3 4 2 5% 5% 16%	1520
December	1st to 10th	Day	16% 30% 9% 16% 3 3 3 3 3 2 11%	1520
	11th to 20th	Day	16% 21% 9% 18% 5% 4 3 3 4 5% 13%	1906
	21st to end	Day	21% 29% 9% 12% 5% 3 3 2 2 3 11%	2772
January	1st to 10th	Night	14% 25% 10% 19% 6% 4 3 2 3 3 9%	4429
	11th to 20th	Night	11% 22% 12% 20% 8% 5% 4 3 3 3 10%	4153
	21st to end	Night	20% 21% 10% 17% 10% 4 3 2 3 2 9%	4532
February	1st to 10th	Night	15% 20% 6% 16% 11% 5% 3 2 3 4 15%	2470
	11th to 20th	Night	11% 17% 9% 19% 9% 5% 5% 2 4 5% 14%	2403
	21st to end	Night	16% 17% 6% 17% 8% 4 4 2 4 3 19%	1951
March	1st to 10th	Night	19% 17% 5% 10% 5% 4 3 2 4 4 27%	3408
	11th to 20th	Night	17% 20% 9% 11% 5% 3 3 2 3 5% 22%	3479
	21st to end	Night	14% 14% 6% 12% 5% 4 3 3 4 5% 31%	3817
April	1st to 10th	Night	17% 17% 6% 8% 5% 4 4 3 4 5% 28%	1912
	11th to 20th	Night	19% 15% 3 6% 4 4 4 3 4 6% 34%	1875
	21st to end	Night	15% 14% 3 6% 5% 5% 4 4 6% 8% 30%	1743
May	1st to 10th	Night	24% 12% 3 7% 4 4 3 3 4 5% 30%	2833
	11th to 20th	Night	14% 12% 4 6% 5% 4 5% 4 5% 7% 33%	2537
	21st to end	Night	14% 8% 2 5% 3 3 4 3 6% 9% 42%	2738
June	1st to 10th	Night	14% 8% 3 8% 5% 4 6% 4 6% 8% 34%	1520
	11th to 20th	Night	13% 7% 3 6% 4 5% 5% 4 7% 8% 39%	1520
	21st to end	Night	14% 7% 3 7% 5% 5% 5% 2 6% 8% 39%	1520
July	1st to 10th	Night	13% 9% 2 7% 5% 4 4 4 5% 7% 40%	2520
	11th to 20th	Night	12% 8% 2 6% 4 4 5% 3 6% 8% 42%	2520
	21st to end	Night	12% 6% 3 6% 5% 4 5% 4 6% 8% 41%	3082
August	1st to 10th	Night	10% 6% 2 6% 4 5% 5% 4 6% 8% 44%	1701
	11th to 20th	Night	14% 7% 3 7% 4 5% 5% 4 7% 8% 36%	1688
	21st to end	Night	12% 8% 2 6% 4 5% 5% 4 6% 9% 40%	2013
September	1st to 10th	Night	16% 8% 3 5% 4 4 3 4 5% 7% 41%	1800
	11th to 20th	Night	15% 7% 2 6% 4 4 4 3 5% 6% 45%	1858
	21st to end	Night	18% 7% 3 8% 5% 5% 4 4 6% 7% 33%	2043
October	1st to 10th	Night	19% 8% 3 7% 5% 4 4 3 4 6% 36%	2160
	11th to 20th	Night	22% 11% 3 8% 5% 4 5% 4 4 6% 28%	2160
	21st to end	Night	28% 15% 3 7% 4 3 4 3 4 5% 24%	2376
November	1st to 10th	Night	16% 17% 4 8% 4 3 3 3 4 5% 32%	2377
	11th to 20th	Night	17% 21% 5% 9% 5% 4 4 5% 4 6% 21%	2660
	21st to end	Night	16% 23% 7% 12% 5% 4 3 3 4 4 18%	2660
December	1st to 10th	Night	18% 28% 10% 13% 6% 3 4 3 3 2 11%	2660
	11th to 20th	Night	17% 23% 10% 17% 5% 4 3 2 3 3 12%	3288
	21st to end	Night	21% 24% 9% 13% 6% 4 4 3 3 3 9%	4884

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	78% 3 7% 8% 3	2518
	11th to 20th	Day	77% 3 6% 10% 4	2790
	21st to end	Day	82% 4 7% 5% 2	3124
February	1st to 10th	Day	76% 4 8% 8% 4	1710
	11th to 20th	Day	71% 4 6% 13% 5%	1672
	21st to end	Day	67% 4 9% 14% 5% 1	1500
March	1st to 10th	Day	59% 4 9% 23% 5%	3435
	11th to 20th	Day	59% 5% 15% 15% 5% 1	3480
	21st to end	Day	59% 4 8% 20% 8% 1	3815
April	1st to 10th	Day	58% 5% 10% 16% 11%	2267
	11th to 20th	Day	52% 6% 10% 19% 11% 1	2254
	21st to end	Day	54% 5% 10% 17% 13% 1	2454
May	1st to 10th	Day	54% 5% 9% 21% 9% 2	4120
	11th to 20th	Day	53% 10% 11% 18% 7% 1	4360
	21st to end	Day	40% 8% 13% 23% 14% 2	4837
June	1st to 10th	Day	48% 6% 12% 20% 13% 2	2660
	11th to 20th	Day	47% 7% 13% 21% 12%	2660
	21st to end	Day	45% 7% 13% 23% 12%	2660
July	1st to 10th	Day	43% 6% 13% 25% 13% 1	4370
	11th to 20th	Day	42% 7% 13% 22% 16%	4365
	21st to end	Day	44% 6% 13% 23% 13% 1	4324
August	1st to 10th	Day	43% 9% 14% 25% 9%	2444
	11th to 20th	Day	49% 9% 13% 21% 7%	2433
	21st to end	Day	44% 8% 12% 25% 9% 1	2533
September	1st to 10th	Day	48% 7% 10% 22% 12% 1	2160
	11th to 20th	Day	43% 6% 12% 24% 14% 1	2098
	21st to end	Day	51% 7% 11% 21% 10% 1	1916
October	1st to 10th	Day	53% 6% 12% 16% 11% 2	1800
	11th to 20th	Day	60% 5% 12% 16% 7% 1	1800
	21st to end	Day	66% 4 10% 12% 7% 1	1980
November	1st to 10th	Day	55% 5% 11% 15% 11% 2	1698
	11th to 20th	Day	64% 5% 10% 13% 6% 2	1520
	21st to end	Day	71% 4 10% 11% 4 1	1520
December	1st to 10th	Day	79% 4 7% 8% 2	1520
	11th to 20th	Day	74% 5% 10% 8% 2 1	1906
	21st to end	Day	79% 4 9% 7% 1	2772
January	1st to 10th	Night	80% 3 8% 7% 3	4429
	11th to 20th	Night	78% 4 8% 7% 2 1	4153
	21st to end	Night	82% 3 5% 7% 2	4532
February	1st to 10th	Night	74% 4 9% 10% 4	2470
	11th to 20th	Night	73% 5% 7% 11% 4	2405
	21st to end	Night	69% 4 8% 12% 7% 1	1951
March	1st to 10th	Night	61% 5% 8% 21% 4	3418
	11th to 20th	Night	64% 4 10% 16% 5%	3480
	21st to end	Night	54% 5% 9% 18% 12% 2	3817
April	1st to 10th	Night	59% 5% 10% 16% 10%	1912
	11th to 20th	Night	52% 6% 11% 17% 13% 2	1875
	21st to end	Night	51% 6% 10% 19% 11% 2	1743
May	1st to 10th	Night	54% 6% 9% 19% 9% 2	2840
	11th to 20th	Night	49% 10% 13% 21% 7% 1	2538
	21st to end	Night	37% 8% 12% 24% 14% 5%	2739
June	1st to 10th	Night	45% 7% 12% 23% 13% 1	1520
	11th to 20th	Night	40% 8% 13% 24% 13% 2	1520
	21st to end	Night	42% 7% 12% 27% 11% 1	1520
July	1st to 10th	Night	43% 5% 13% 22% 15% 2	2480
	11th to 20th	Night	39% 5% 16% 26% 13% 1	2472
	21st to end	Night	40% 6% 15% 23% 16% 1	2984
August	1st to 10th	Night	37% 8% 15% 30% 9% 1	1690
	11th to 20th	Night	42% 9% 16% 24% 9%	1688
	21st to end	Night	38% 8% 15% 26% 11% 2	2013
September	1st to 10th	Night	41% 7% 14% 24% 12% 2	1800
	11th to 20th	Night	38% 6% 14% 25% 16% 1	1858
	21st to end	Night	48% 8% 12% 19% 12% 1	2043
October	1st to 10th	Night	48% 6% 12% 19% 14% 1	2160
	11th to 20th	Night	55% 6% 12% 16% 9% 1	2160
	21st to end	Night	62% 5% 11% 14% 7% 1	2376
November	1st to 10th	Night	51% 6% 11% 19% 10% 3	2377
	11th to 20th	Night	63% 5% 11% 13% 6% 3	2660
	21st to end	Night	69% 5% 11% 12% 3	2660
December	1st to 10th	Night	81% 4 6% 7% 2	2660
	11th to 20th	Night	77% 3 9% 8% 2	3288
	21st to end	Night	80% 5% 8% 7% 1	4884

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	30% 31% 26% 10% 3 1	180
	11th to 20th	Day	36% 33% 23% 6% 2	258
	21st to end	Day	29% 31% 28% 10% 2	297
February	1st to 10th	Day	39% 26% 30% 5% 1	270
	11th to 20th	Day	34% 33% 29% 3 1	270
	21st to end	Day	43% 24% 26% 5% 1	300
March	1st to 10th	Day	34% 23% 28% 13% 3	460
	11th to 20th	Day	31% 26% 30% 10% 2 1	460
	21st to end	Day	37% 22% 24% 13% 4 1	506
April	1st to 10th	Day	32% 24% 25% 14% 5% 1	460
	11th to 20th	Day	34% 23% 23% 11% 7% 2	452
	21st to end	Day	29% 19% 32% 15% 4 1	460
May	1st to 10th	Day	33% 20% 25% 15% 6% 2	463
	11th to 20th	Day	26% 15% 28% 21% 9% 1	487
	21st to end	Day	16% 15% 30% 21% 13% 5%	529
June	1st to 10th	Day	22% 18% 30% 20% 9% 2	490
	11th to 20th	Day	20% 12% 28% 24% 14% 2	490
	21st to end	Day	19% 14% 36% 22% 8% 1	490
July	1st to 10th	Day	12% 10% 31% 24% 17% 6%	485
	11th to 20th	Day	14% 10% 28% 27% 16% 5%	484
	21st to end	Day	13% 9% 37% 24% 13% 4	532
August	1st to 10th	Day	13% 9% 29% 26% 15% 8%	486
	11th to 20th	Day	17% 9% 28% 24% 14% 8%	479
	21st to end	Day	16% 11% 27% 24% 15% 8%	532
September	1st to 10th	Day	21% 11% 23% 23% 15% 7%	450
	11th to 20th	Day	16% 9% 25% 21% 22% 8%	450
	21st to end	Day	20% 17% 27% 17% 14% 5%	450
October	1st to 10th	Day	25% 13% 26% 17% 14% 4	450
	11th to 20th	Day	31% 20% 28% 14% 6% 1	450
	21st to end	Day	39% 16% 27% 16% 2	495
November	1st to 10th	Day	29% 19% 27% 17% 6% 3	354
	11th to 20th	Day	41% 20% 26% 9% 2 1	180
	21st to end	Day	36% 24% 32% 7% 1	180
December	1st to 10th	Day	43% 23% 23% 5% 4 1	180
	11th to 20th	Day	39% 25% 28% 6% 1	180
	21st to end	Day	40% 24% 32% 3 1	198
January	1st to 10th	Night	31% 29% 26% 11% 3	760
	11th to 20th	Night	31% 26% 28% 13% 2	760
	21st to end	Night	25% 28% 30% 14% 2	836
February	1st to 10th	Night	30% 26% 29% 15% 1	760
	11th to 20th	Night	29% 28% 32% 11% 1	743
	21st to end	Night	32% 25% 29% 12% 2	628
March	1st to 10th	Night	28% 21% 34% 14% 3	760
	11th to 20th	Night	34% 20% 24% 17% 4 1	760
	21st to end	Night	25% 20% 33% 15% 6% 1	836
April	1st to 10th	Night	28% 19% 30% 20% 3	760
	11th to 20th	Night	30% 17% 27% 19% 7% 1	751
	21st to end	Night	22% 13% 31% 28% 6%	603
May	1st to 10th	Night	22% 12% 24% 29% 12%	570
	11th to 20th	Night	16% 11% 29% 35% 8%	403
	21st to end	Night	16% 9% 24% 32% 17% 2	411
June	1st to 10th	Night	16% 6% 27% 36% 13% 1	380
	11th to 20th	Night	18% 9% 23% 38% 12%	380
	21st to end	Night	16% 6% 31% 33% 14%	380
July	1st to 10th	Night	12% 6% 17% 45% 16% 4	370
	11th to 20th	Night	11% 3 24% 38% 23% 1	368
	21st to end	Night	15% 4 21% 36% 24% 1	619
August	1st to 10th	Night	13% 4 20% 35% 27% 2	567
	11th to 20th	Night	15% 5% 18% 30% 29% 2	564
	21st to end	Night	13% 6% 21% 35% 22% 2	765
September	1st to 10th	Night	19% 8% 20% 30% 21% 2	720
	11th to 20th	Night	16% 8% 18% 27% 26% 4	720
	21st to end	Night	21% 11% 21% 26% 17% 3	720
October	1st to 10th	Night	24% 11% 24% 23% 16% 2	720
	11th to 20th	Night	29% 15% 29% 21% 6%	720
	21st to end	Night	36% 16% 27% 18% 3	792
November	1st to 10th	Night	27% 15% 28% 24% 7%	740
	11th to 20th	Night	31% 20% 27% 16% 5% 1	760
	21st to end	Night	30% 23% 28% 14% 4	760
December	1st to 10th	Night	36% 25% 26% 11% 3	760
	11th to 20th	Night	33% 25% 27% 12% 2	760
	21st to end	Night	34% 24% 30% 12% 1	836

Page generated at 2024-08-27 09:49:43. Version ac07

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